1. Field of the Invention
This invention relates generally to air valves, and more particularly, to a three-way, normally closed only, pilot valve for use in controlling the flow of pilot air to a directional flow control valve for operating the main spool valve thereof. The type of directional flow control valves which may be controlled by the pilot valve of the present invention includes four-way valves, three-way valves, two-way valves, and the like.
2. Description of the Prior Art
It is known in the air valve art to provide solenoid operated pilot air valves for use in controlling the flow of pilot air to directional flow control valves. A disadvantage of the prior art pilot air valves is that they require at least two dynamic air seals. A further disadvantage of the prior air pilot air valves is that they include a valve spool which is shifted in one direction by a solenoid, and shifted in the other direction by a return spring when the solenoid is de-energized. Another disadvantage of the prior art pilot air valves as if they are of the poppet type they are balanced and subject to pressure limitations based on orifice size. If they are of the balanced spool type they require no longer solenoid strokes and have at least three dynamic seals. If they are of the balanced spool-poppet type, as shown in U.S. Pat. No. 3,538,954, they have the short solenoid stroke of the poppet type but have two dynamic air seals.